The present invention relates to a novel tool which allows boring, skiving and roller burnishing of a cylindrical hole in a single pass. The tool includes means for remotely actuating a rotary skiving knife simultaneously with the roller burnishing tool.
Rotary skiving tools are used to accurately cut small quantities of material from the wall of a cylindrical hole. After the skiving tool has made a pass through the workpiece it is usually drawn back through the newly worked hole. If the knife blades on the skiving tool are not retracted the blades will scratch or score the surface of the hole. This is totally unacceptable when unmarred finishes are needed, for example in hydraulic cylinders.
Retractable rotary skiving knives have been developed so that the knife blades do not score the cylinder wall (see, for example, U.S. Pat. No. 3,795,957). These tools typically use a knife holder having two knife blades. The knife blades are pulled inwardly by springs and are extended by pulling (or pushing) a shifting rod having a tapered end, against which the knife blades rest, to wedge the knife blades apart. Pushing (or pulling) the shifting rod allows the springs to pull the blades inwardly so the tool can be withdrawn from the workpiece. The distance the blades extend is determined by the distance the shifting rod moves and the angle of the tapered end. With this arrangement the radial forces on the knife blades are transmitted from the knife blades to the shifting rod to produce axial forces on the shifting rod. The extended position of the knife blades can vary, possibly resulting in an out-of-tolerance hole, depending upon several factors including the rigidity with which the shifting rod is locked into place and the amount of relative movement which occurs between the mating surfaces of the tapered end of the shifting rod and the knife blades. Further, centrifugal forces on the rotating knife tend to urge the knife blades outwardly in opposition to the springs.
Roller burnishing tools utilize a plurality of circumferentially spaced rollers in a roller cage to roller burnish the interior of a pre-formed cylindrical hole so that it has a smooth finish. Tools of this type are available in which rollers are located on a race which is inclined radially outwardly toward the rear, and a manually adjustable stop is provided which restricts the rearward movement of the rollers up the inclined race. Tools utilizing roller burnishers of this type are illustrated in a brochure of the Hegenscheidt Corporation, having a U.S. office at 1070 Livernois Avenue, Troy, Mich. 48084 entitled The Combined Skiving and Roller Finishing Tools, Type RDS RETRAC, and U.S. Pat. Nos. 3,795,957; 3,980,442 and 4,133,089.
When roller burnishing tools of the type described above are inserted in a cylinder, the forward thrust of the tool causes the rollers to move upwardly along the inclined race until the race contacts the preset stop. Accordingly, for all practical purposes, the rollers have a preset radius depending on the position of the stop.
Roller burnishing tools of the type just described, i.e. those having effectively fixed radii, are generally satisfactory when the interior of the cylinder to be burnished is very close to the preset diameter of the tool. They are, however, are unsatisfactory when the actual inside diameter of the cylinder deviates substantially (either larger or smaller) from the nominal diameter. To overcome this drawback, roller burnishing tools have been provided in which the roller bearing race is inclined radially outward in the operative direction of the tool. The rollers are enclosed in a roller cage which is used to urge the rollers in the operative direction so that they translate radially outward until they engage the interior of the cylinder. In this way, as the tool is pushed (or drawn) through the cylinder, the rollers may be held against the interior of the cylinder by the roller cage, conforming to any slight deviations in the interior diameter. Such roller burnishing tools are disclosed in U.S. Pat. Nos. 3,791,000 and 3,656,333.
Although an improvement over roller burnishing tools which are unable to adapt to variations in the internal diameter of the workpiece, such adjustable roller burnishing tools suffer from certain drawbacks. In particular, the use of a roller cage having a plurality of slots for engaging the individual rollers and holding the rollers in place on the conical roller bearing surface as the tool is advanced through the workpiece often causes binding between the rollers and the cage (preventing the roller from rolling) and can lead to excessive wear both on the roller cage and on the individual rollers.
Skiving tools are often used in combination with a roller burnishing tool so that the skiving tool first cuts or shaves off a small amount of material from the hole and then the roller burnishing tool, mounted coaxially on the same drive shaft with the skiving tool, burnishes the hole to a smooth finish. Such combination tools are disclosed in U.S. Pat. Nos. 3,795,957; 3,980,442; and 4,133,089.
Heretofore combined skiving and burnishing tools which have included retractable rotary skiving knives have typically resembled the tool disclosed in U.S. Pat. No. 3,980,442 and included non-retractable blades in combination with a roller burnishing tool of the type described hereinbefore. Such tools are undesirable for the reasons previously set forth concerning skiving tools having non-retractable blades, i.e. non-retractable blades often scratch or score the inside surface of the work piece. A combined skiving and burnishing tool which does include retractable rotary skiving knivings is described in copending application Ser. No. 401,580, in the name of the present inventor.
The skiving tools, roller burnishing tools, and combined skiving and roller burnishing tools just described are all limited in their ability to remove relatively large amounts of material from the cylindrical hole being finished. A conventional skiving tool can remove at most about 0.1 inches from the cylindrical wall, and usually is used to remove about 0.01 inches or less. Burnishing tools, of course, act only to smooth and polish the cylindrical wall and do not remove substantial amounts of material at all. Often, it is necessary to remove much larger amounts of material from the cylindrical wall, often as much as 0.5 inches in the radial direction, or more. Heretofore, when such large amounts of materials were required to first bore out the cylindrical hole using a conventional boring tool, after completing the boring operation, the user then had to employ a skiving tool and a burnishing tool, or a combined skiving and burnishing tool, to finish the cylindrical hole within the tolerances required. The need to complete two or three such separate fabricating operations necessarily increased the time required for finishing the cylinder. Thus, it would be desirable to provide a single tool capable of effecting the boring, skiving, and roller burnishing operations in a single pass. It would be particularly desirable to provide such a tool having retractable skiving knives so that the tool can be withdrawn with the knives retracted to prevent damage to the newly finished cylindrical wall.